The content of formaldehyde in squid is high and formaldehyde can cross-link with protein， which leads to the decrease of protein quality. It is of great significance to delay the decrease of protein by adding some natural products. The squid muscle-TMAOase simulation system was constructed to investigate the effect of catechin on protein functional properties in squid muscle. The changes of color difference value， water holding capacity， solubility， particle size， turbidity， gelation ability and gel strength were measured. At the same time， the effects of （+）-catechins on the functional properties of squid protein were discussed. The results showed that （+）-catechins had an inhibitory effect on TMAO decreasing and significantly reduced the content of FA and DMA. Catechin protects the color of squid meat. Low concentration of catechins （20， 40， 60 μmol/g） could promote the solubility and gelation of squid MP， and it could inhibit the increase of turbidity and increase of particle size. High concentrations of （+）-catechins （80， 100 μmol/g） could inhibit the functional properties of squid myofibrillar protein. Therefore， the optimal catechin addition for maintaining protein functional properties was 60 μmol/g.